Mechanical and chemical-mechanical planarization processes remove material from the surfaces of semiconductor wafers, field emission displays and many other microelectronic substrates to form a flat surface at a desired elevation. FIG. 1 schematically illustrates a planarizing machine 10 with a platen or base 20, a carrier assembly 30, a planarizing medium 40, and a planarizing solution 44 on the planarizing medium 40. The planarizing machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 for supporting the planarizing medium 40. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to move the planarizing medium 40 during planarization.
The carrier assembly 30 controls and protects a substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 with a pad 34 that holds the substrate 12 via suction, and an actuator assembly 36 typically rotates and/or translates the substrate holder 32 (arrows C and D, respectively). However, the substrate holder 32 may be a weighted, free-floating disk (not shown) that slides over the planarizing medium 40.
The planarizing medium 40 and the planarizing solution 44 may separately, or in combination, define a polishing environment that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing medium 40 may be a conventional polishing pad made from a relatively compressible, porous continuous phase matrix material (e.g., polyurethane), or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension medium. In a typical application, the planarizing solution 44 may be a chemical-mechanical planarization slurry with abrasive particles and chemicals for use with a conventional non-abrasive polishing pad, or the planarizing solution 44 may be a liquid without abrasive particles for use with an abrasive polishing pad.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against a planarizing surface 42 of the planarizing medium 40 in the presence of the planarizing solution 44. The platen 20 and/or the substrate holder 32 then move relative to one another to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the polishing environment remove material from the surface of the substrate 12.
Planarizing processes must consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns on the substrate. As the density of integrated circuits increases, the uniformity and planarity of the substrate surface is becoming increasingly important because it is difficult to form sub-micron features or photo-patterns to within a tolerance of approximately 0.1 .mu.m when the substrate surface is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface on the substrate.
In the competitive semiconductor and microelectronic device manufacturing industries, it is also desirable to maximize the yield of individual devices or dies on a substrate. Typical semiconductor manufacturing processes fabricate a plurality of dies (e.g., 50-250) on each substrate. To increase the number of dies that are fabricated on each substrate, many manufacturers are increasing the size of the substrates to provide more surface area for fabricating additional dies. Thus, to maximize the yield of operable dies on each substrate, planarizing processes should produce a uniformly planar surface across the entire substrate.
In conventional planarizing processes, the substrate surface may not be uniformly planar because the rate at which material is removed from the substrate surface (the "polishing rate") typically varies from one region on the substrate to another. The polishing rate is a function of several factors, and many of the factors may change during planarization. For example, some of the factors that effect the polishing rate across the substrate surface are as follows: (1) the distribution of abrasive particles and chemicals between the substrate surface and the planarizing medium; and (2) the condition of the planarizing surface on the planarizing medium.
To reduce deviations in the uniformity of the substrate surface, several existing planarizing media are polishing pads with holes or grooves that transport a portion of the planarizing solution below the substrate surface during planarization. A Rodel IC-1000 polishing pad, for example, is a relatively soft, porous polyurethane pad with a number of large slurry wells approximately 0.05-0.10 inches in diameter that are spaced apart from one another across the planarizing surface by approximately 0.125-0.25 inches. During planarization, small volumes of slurry are expected to fill the large wells, and then hydrodynamic forces created by the motion of the substrate are expected to draw the slurry out of the wells in a manner that wets the substrate surface. U.S. Pat. No. 5,216,843 describes another polishing pad with a plurality of macro-grooves formed in concentric circles and a plurality of micro-grooves radially crossing the macro-grooves. In such grooved pads, it is expected that the grooves hold a portion of the planarizing solution below the substrate surface during planarization.
Although polishing pads with holes or grooves improve the uniformity of substrate surfaces, they may not produce adequately uniform surfaces on substrates after several planarizing and conditioning cycles. One factor affecting the uniformity of the substrate surface is the condition of the polishing pad. The planarizing surface of the polishing pad typically deteriorates after polishing a number of substrates because waste matter from the substrate, planarizing solution and/or the polishing pad accumulates on the planarizing surface. For example, when a doped silicon glass layer is planarized, a portion of the glass glazes over areas of the planarizing surface. The waste matter typically does not accumulate uniformly across the planarizing surface, and thus the waste matter alters local polishing rates across the pad. Polishing pads are accordingly "conditioned" by removing the waste matter from the pad to restore the polishing pad to a suitable condition for planarizing substrates.
Polishing pads are conventionally conditioned with devices that contact the waste matter with an abrasive element or a water jet to remove the waste matter from the pad. One conventional method for conditioning polishing pads is to abrade the planarizing surface with a diamond end-effector that abrades the waste matter accumulations and exposes portions of the planarizing surface on top of the polishing pad. Another conventional method is to spray the polishing pad with a jet of deionized water that separates the waste matter accumulations from the polishing pad.
Conditioning polishing pads with the existing methods, however, may produce deviations in the uniformity of the substrate surface because it is difficult to consistently condition a polishing pad so that it has the same planarizing characteristics from one conditioning cycle to the next. For example, diamond end-effectors and water jets are surface contact elements that may not remove waste matter embedded in depressions below the planarizing surface (e.g., holes, pores or grooves). Conventional conditioning systems accordingly may not return such polishing pads to a state in which they can hold an adequate amount of planarizing solution below the substrate surface. Another concern of conventional conditioning systems is that diamond end-effectors may produce a non-planar surface on a polishing pad because they remove material from exposed areas on the planarizing surface while removing waste matter from covered areas on the planarizing surface. As such, diamond end-effectors may produce low points in the planarizing surface that were exposed at an early stage of a conditioning cycle. Conventional conditioning systems, therefore, may not return polishing pads and other planarizing media to a condition in which they uniformly planarize substrate surfaces.